Display panel or portion thereof with a transitional graphical user interface



FIG. 1 is a front view of a display panel or portion thereof with a graphical user interface showing a first image in a sequence of a design; and,

FIG. 2 is a front view of a display panel or portion thereof with a graphical user interface showing a second image in the sequence of the design.

The appearance of the image sequentially transitions between the images shown in FIGS. 1 to 2 . The process or period in which image transitions to another forms no part of the claimed design.

The outermost broken line illustrates a display panel or portion thereof that forms no part of the claimed design. The remaining broken lines, including all text, illustrate portions of a graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display panel or portion thereof with a transitional graphical user interface, as shown and described. 